1. Technical Field
The present invention relates to a line head and an image-forming apparatus.
2. Related Art
A line printer (i.e., an image-forming apparatus) is known as a printer employing an electrophotographic method. The line printer has a structure in which a charger, a line-shaped printer head (i.e., a line head), a developing device, a transfer device, etc., are arranged closely to each other on the circumferential surface of a photosensitive drum used as a part to be exposed. In the line printer, an exposure spot that is turned into an electrostatic latent image is formed on the circumferential surface of the photosensitive drum electrostatically charged by the charger while exposing the photosensitive drum through a selective light-emitting operation of light emitting devices disposed on the printer head. The latent image is then developed with a toner supplied from the developing device, and a resulting toner image is transferred to a sheet of paper by the transfer device.
An image-forming apparatus in which a light-emitting device array that has organic electroluminescence devices (organic EL devices) serving as light-emitting devices is used as a printer head is known as the thus structured line printer (see Japanese Unexamined Patent Application, First Publication No. 2005-119104, for example).
In the line head disclosed in JP 2005-119104, relatively expanded light is projected from the organic EL devices onto a photosensitive drum, and hence the light becomes relatively low in brightness (i.e., in intensity), thus making it difficult to sufficiently expose the photosensitive drum. For example, a possible method for obtaining point-like light having high brightness is to pass a large amount of electric current through the small organic EL devices. However, according to this method, high heat is generated in the organic EL devices in accordance with the amount of the electric current, and deteriorates the organic EL devices used as light emitting devices, thus shortening the life of each of the organic EL devices.